Metal powder for powder metallurgy and iron-based sintered compact

ABSTRACT

Provided is metallic powder for powder metallurgy having iron as its principal component and containing indium soap, or metallic powder for powder metallurgy further comprising at least one type selected among bismuth soap, nickel soap, cobalt soap, copper soap, manganese soap and aluminum soap in such indium soap. Thereby obtained is metallic powder for powder metallurgy capable of easily improving the rustproof effect without having to hardly change the conventional process.

TECHNICAL FIELD

The present invention pertains to mixed powder for powder metallurgy tobe employed in the manufacture of sintered components, blushes and soon, and particularly to metallic powder for powder metallurgy and aniron-based sintered body suitable in manufacturing the likes ofiron-based sintered components superior in rustproof performance to beused as a solid lubricant or the like.

BACKGROUND ART

Generally, iron powder used in the application of sintered mechanicalcomponents, sintered oil retaining bearings, metal graphite brushes andso on rusts easily, and is commonly used upon mixing an organicrust-prevention agent such as benzotriazole therein.

Nevertheless, although such an organic rust-prevention agent possesses atemporary rustproof effect, it decomposes or evaporates at 500° C. orhigher, and becomes lost at an ordinarily employed sintering temperatureof 700° C. or higher. Therefore, the same condition will occur unlessrust prevention is performed after the sintering, and there is a problemin that the sintered object will rust easily.

Meanwhile, in order to obtain the rustproof performance after sintering,a proposal has been made to form a composite powder sintered body bymixing a slight amount of metal powder such as zinc, bismuth, lead orthe like with sintering powder having iron as its principal component,or mixing the vapor thereof to the gas used during sintering.

However, this requires an additional step, the manufacturing processwill become complex as a result thereof, and there is a problem in thatthere will be variations in the quality all that much more. Further,even if metal powder of bismuth or lead is mixed in, minute particlesare merely dispersed, and it could not be said that it is evenlydistributed. Further, since indium metal is a soft metal, it isdifficult to make it into metal powder.

As a conventional additive agent for powder metallurgy, there is anadditive agent having organic acid cobalt metallic soap as itscomponent, and technology for manufacturing a sintered body by addingand mixing this additive agent 0.1 to 2.0% by weight, and then moldingand sintering this mixed powder has been disclosed (c.f. Japanese PatentLaid-Open Publication No. H10-46201).

Moreover, technology of adding and mixing metal stearate to rareearth-iron-boron permanent magnet coarse powder, which is mainlycomposed in atomic % of rare earth element R (among rare-earth elementscontaining Y, one or two or more elements are combined) of 10 to 25%,boron B of 1 to 12%, and the remaining part consisting of iron Fe (apart of Fe is replaced at least with one or more kinds of elementsselected from Co, Ni, Al, Nb, Ti, W, Mo, V, Ga, Zn and Si in a range of0 to 15%, if necessary), and thereafter dry-pulverizing this mixture hasalso been disclosed (c.f. Japanese Patent Laid-Open Publication No.H6-290919).

Further, a molding improving agent of alloy powder for a permanentmagnet consisting of at least one kind selected from polyoxyethylenealkyl ether, polyoxyethylene monofatty acid ester and polyoxyethylenealkylallylether compounded with at least on kind of stearate at 1/20 to5/1 compounding ratio has also been disclosed (c.f. Japanese PatentLaid-Open Publication No. S61-34101).

DISCLOSURE OF THE INVENTION

An object of the present invention is to provide metallic powder forpowder metallurgy capable of easily improving the rust-prevention effectwithout having to hardly change the conventional process, and aniron-based sintered body with a rustproof function obtained by sinteringsuch metallic powder for powder metallurgy.

As a result of intense study to resolve the foregoing problems, thepresent inventors discovered that by mixing a specific additive materialduring molding of the sintering powder having iron as its principalcomponent, an effect as a lubricant during molding can be yielded, andthe rust-prevention effect of products after sintering could besignificantly improved by dispersing the metal component evenly.

Based on this discovery, the present invention provides:

-   1. Metallic powder for powder metallurgy having iron as its    principal component, characterized in containing indium soap;-   2. Metallic powder for powder metallurgy according to paragraph 1    above, characterized in further comprising at least one type    selected among bismuth soap, nickel soap, cobalt soap, copper soap,    manganese soap and aluminum soap;-   3. An iron-based sintered body with a rustproof function obtained by    adding indium soap to metallic powder for powder metallurgy having    iron as its principal component, and sintering this mixture; and-   4. An iron-based sintered body with a rustproof function obtained by    adding and sintering indium soap, and further adding and sintering    at least one type selected among bismuth soap, nickel soap, cobalt    soap, copper soap, manganese soap and aluminum soap.    Mode for Carrying Out the Invention

Upon devising the present invention, the present inventors focusedattention on zinc stearate to be added in a slight amount as a lubricantupon forming powder. Nevertheless, this zinc stearate has a problem inthat it dissipates during sintering, and damages the sintering furnacesince it has high corrosiveness, and it has become evident that therustproof effect is hardly any different from a case when it isadditive-free.

As described above, in most cases, this zinc stearate is merely used asa lubricant upon molding, and materials were considered which possess anequal lubricant function as this zinc stearate and at the same timecapable of increasing the rustproof effect unavailable in such zincstearate.

Here, added to the metallic powder for powder metallurgy was metallicsoap having a function as a molding lubricant equivalent to that of zincstearate, which possesses suitable vapor pressure at the sinteringtemperature, and which is capable of improving the rustproof effect evenafter sintering.

As a result, the rustproof effect of a sintered body can be improvedexponentially without having to significantly change the conventionalmanufacturing process of such sintered body.

It has become known that indium soap possessing suitable vapor pressurein this sintering temperature yields an extremely superior rustproofeffect. Moreover, a similar rustproof effect could be obtained byfurther adding to this indium soap a soap selected from bismuth soap,nickel soap, cobalt soap, copper soap, manganese soap and aluminum soap.

Moreover, metallic soaps such as metallic soap stearate, metallic soappropionate and metallic soap naphthenate may be used as the soap.

Generally, it is desirable to add 0.1 to 2.0 parts by weight of suchmetallic soap to 100 parts by weight of metallic powder for powdermetallurgy having iron as its principal component.

Nevertheless, this additive amount may be changed in accordance with thetype of sintered body, and the additive amount does not necessarily haveto be limited to the foregoing additive amount. In other words, theadditive amount may be arbitrarily set within a range that is capable ofmaintaining the characteristics of the target sintered body.

Further, the metallic powder for powder metallurgy to which metallicsoap is added does not necessarily have to be iron powder, and thepresent invention may be similarly applied to powder in which iron iscoated on other metal powders or an iron-mixed powder for improving therustproof effect.

EXAMPLES AND COMPARATIVE EXAMPLES

Next, the present invention is described based on the Examples. TheExamples are for facilitating the understanding of the invention, andthe present invention is not in any way limited thereby. In other words,the present invention covers other Examples and modifications based onthe technical spirit of the invention.

Example 1

Synthesized indium stearate (In content of 12.0 wt %) was pulverized,and this was put through a sieve to obtain fine powder of 250 meshes orless.

0.8 wt % of this indium stearate (abbreviated as “In” in Table 1 below)and 1.0 wt % of graphite powder were mixed with the iron powder(Hoganas-made: reduced iron powder). This mixed powder (fill of 15 to2.5 g) was molded into a test piece of approximately 10.06 mm φ×2.70 to4.55 mmH under a molding pressure of 6 t/cm².

In order to judge moldability, details of the relationship and the likeof the molding density (GD) and molding pressure of the respectivecompacts are shown in Table 1 (Sample No. 291 to 298).

Evaluation on the moldability of the mixed powder was conducted withrespect to the test piece, and, in addition, the compact molded intothis test piece was sintered in a batch type atmospheric furnace at asintering temperature of 1150° C., sintering time of 60 min., and undera hydrogen gas atmosphere. The density (SD) and the like of the sinteredbody are similarly shown in Table 1.

This sintered body was set inside a constant temperature and humiditychamber, and an atmospheric exposure test was conducted for 336 hours ata temperature of 40° C. and humidity of 95% in order to conduct amoisture and oxidation resistance experiment. The results of themoisture and oxidation resistance experiment are shown in Table 2. TABLE1 After Sintering at Pressure Before Sintering 1150° C., 1 hr, H2 SampleFill Pressure (Device Side) φ t w GD Sintering φ t w SD No. No. Soap g t· cm−2 kgf · cm−2 mm mm g g/cc Batch mm mm g g/cc 291 (9) In 1.5 6 42010.07 2.71 1.48 6.86 4-4 10.04 2.69 1.46 6.86 292 (9) In 1.5 6 420 10.082.7 1.48 6.87 4-4 10.05 2.69 1.46 6.84 293 (9) In 2.5 6 420 10.07 4.522.46 6.83 4-4 10.05 4.5 2.44 6.84 294 (9) In 2.5 6 420 10.07 4.54 2.466.80 4-4 10.05 4.51 2.46 6.88 295 (9) In 2.5 6 420 10.08 4.5 2.47 6.884-4 10.05 4.47 2.45 6.91 296 (9) In 2.5 6 420 10.06 4.55 2.5 6.91 4-410.05 4.53 2.48 6.90 297 (9) In 2.5 6 420 10.06 4.52 2.47 6.87 4-4 10.064.51 2.46 6.86 298 (9) In 2.5 6 420 10.06 4.52 2.49 6.93 4-4 10.06 4.52.46 6.88

TABLE 2 Oxidation Resistance Additive Agent After 96 Hours After 168Hours After 336 Hours Example 1 In Stearate No change in color Slightchange in color Slight change in color Example 2 In Stearate + Bi Nochange in color Slight change in color Slight change in color Example 3In Stearate + Ni No change in color Slight change in color Slight changein color Example 4 In Stearate + Co No change in color Slight change incolor Slight change in color Example 5 In Stearate + Cu No change incolor Slight change in color Slight change in color Example 6 InStearate + Mn No change in color Slight change in color Slight change incolor Comparative Example 1 Zn Stearate Some change in color Severechange in color Severe change in color Comparative Example 2 Sr StearateSevere change in color Severe change in color Severe change in colorComparative Example 3 Ba Stearate Some change in color Severe change incolor Severe change in color Comparative Example 4 Re Stearate Severechange in color Severe change in color Severe change in colorComparative Example 5 Additive Free Some change in color Severe changein color Severe change in color

Example 2

Synthesized bismuth stearate (Bi content of 12.0 wt %) was pulverized,and this was put through a sieve to obtain fine powder of 250 meshes orless.

0.4 wt % of this bismuth stearate (abbreviated as “Bi” in Table 3below), 0.4 wt % of the indium stearate obtained in Example 1 and 1.0 wt% of graphite powder were mixed with the iron powder (Hoganas-made:reduced iron powder). This mixed powder (fill of 1.5 to 2.5 g) wasmolded into a test piece of approximately 10.05 mm φ×2.74 to 4.59 mmHunder a molding pressure of 6 t/cm².

In order to judge moldability, details of the relationship and the likeof the molding density (GD) and molding pressure of the respectivecompacts are shown in Table 3 (Sample No. 281 to 288). Further, althoughthe indium soap added together is not indicated in this Table, 0.4 wt %of indium stearate is contained therein.

Evaluation on the moldability of the mixed powder was conducted withrespect to the test piece under the same conditions as Example 1, and,in addition, the compact molded into this test piece was sintered in abatch type atmospheric furnace at a sintering temperature of 1150° C.,sintering time of 60 min., and under a hydrogen gas atmosphere. Thedensity (SD) and the like of the sintered body are similarly shown inTable 3.

This sintered body was set inside a constant temperature and humiditychamber, and an atmospheric exposure test was conducted for 336 hours ata temperature of 40° C. and humidity of 95% in order to conduct amoisture and oxidation resistance experiment. The results of themoisture and oxidation resistance experiment are shown in Table 2. TABLE3 After Sintering at Pressure Before Sintering 1150° C., 1 hr, H2 SampleFill Pressure (Device Side) φ t w GD Sintering φ t w SD No. No. Soap g t· cm−2 kgf · cm−2 mm mm g g/cc Batch mm mm g g/cc 281 (4) Bi 1.5 6 42010.05 2.76 1.47 6.71 4-3 10.05 2.74 1.49 6.86 282 (4) Bi 1.5 6 420 10.082.74 1.47 6.72 4-3 10.05 2.7 1.49 6.96 283 (4) Bi 2.5 6 420 10.07 4.552.48 6.84 4-3 10.07 4.54 2.49 6.89 284 (4) Bi 2.5 6 420 10.05 4.55 2.476.84 4-3 10.06 4.52 2.49 6.93 285 (4) Bi 2.5 6 420 10.05 4.55 2.47 6.844-3 10.07 4.54 2.5 6.91 286 (4) Bi 2.5 6 420 10.05 4.59 2.5 6.87 4-310.07 4.58 2.52 6.91 287 (4) Bi 2.5 6 420 10.06 4.6 2.5 6.84 4-3 10.064.57 2.52 6.94 288 (4) Bi 2.5 6 420 10.07 4.59 2.5 6.84 4-3 10.07 4.572.51 6.90

Example 3

Synthesized nickel stearate Pi content of 12.0 wt %) was pulverized, andthis was put through a sieve to obtain fine powder of 250 meshes orless.

0.4 wt % of this nickel stearate (abbreviated as “Ni” in Table 4 below),0.4 wt % of the indium stearate obtained in Example 1 and 1.0 wt % ofgraphite powder were mixed with the iron powder (Hoganas-made: reducediron powder). This mixed powder (fill of 1.5 to 2.5 g) was molded into atest piece of approximately 9.93 mm Ox 2.59 to 4.48 mmH under a moldingpressure of 6 t/cm².

In order to judge moldability, details of the relationship and the likeof the molding density (GD) and molding pressure of the respectivecompacts are shown in Table 4 (Sample No. 221 to 228). Further, althoughthe indium soap added together is not indicated in this Table, 0.4 wt %of indium stearate is contained therein.

Evaluation on the moldability of the mixed powder was conducted withrespect to the test piece under the same conditions as Example 1, and,in addition, the compact molded into this test piece was sintered in abatch type atmospheric furnace at a sintering temperature of 1150° C.,sintering time of 60 min., and under a hydrogen gas atmosphere. Thedensity (SD) and the like of the sintered body are similarly shown inTable 4.

This sintered body was set inside a constant temperature and humiditychamber, and an atmospheric exposure test was conducted for 336 hours ata temperature of 40° C. and humidity of 95% in order to conduct amoisture and oxidation resistance experiment. The results of themoisture and oxidation resistance experiment are shown in Table 2.

Moreover, in addition to nickel stearate, the same results were obtainedwith nickel propionate and nickel naphthenate under the same conditions.TABLE 4 After Sintering at Pressure Before Sintering 1150° C., 1 hr, H2Sample Fill Pressure (Deviceside) φ t w GD Sintering φ t w SD No. No.Soap g t · cm−2 kgf · cm−2 mm mm g g/cc Batch mm mm g g/cc 221 (5) Ni1.5 6 420 9.93 2.59 1.5 7.48 4-1 9.88 2.54 1.48 7.60 222 (5) Ni 1.5 6420 9.97 2.69 1.55 7.38 4-1 9.9 2.64 1.53 7.53 223 (5) Ni 2.5 6 420 9.944.44 2.5 7.26 4-1 9.89 4.43 2.48 7.29 224 (5) Ni 2.5 6 420 9.96 4.382.46 7.21 4-1 9.88 4.27 2.44 7.32 225 (5) Ni 2.5 6 420 9.95 4.48 2.57.18 4-1 9.9 4.35 2.47 7.44 226 (5) Ni 2.5 6 420 9.96 4.39 2.45 7.16 4-19.9 4.31 2.45 7.38 227 (5) Ni 2.5 6 420 9.95 4.48 2.51 7.21 4-1 9.894.44 2.51 7.36 228 (5) Ni 2.5 6 420 9.96 4.37 2.47 7.25 4-1 9.87 4.342.46 7.41

Example 4

Synthesized cobalt stearate (Co content of 12.0 wt %) was pulverized,and this was put through a sieve to obtain fine powder of 250 meshes orless.

0.4 wt % of this cobalt stearate (abbreviated as “Co” in Table 5 below),0.4 wt % of the indium stearate obtained in Example 1 and 1.0 wt % ofgraphite powder were mixed with the iron powder (Hoganas-made: reducediron powder). This mixed powder (fill of 1.5 to 2.5 g) was molded into atest piece of approximately 9.96 mm 4×2.64 to 4.47 mmH under a moldingpressure of 6 t/cm².

In order to judge moldability, details of the relationship and the likeof the molding density (GD) and molding pressure of the respectivecompacts are shown in Table 5 (Sample No. 231 to 238). Further, althoughthe indium soap added together is not indicated in this Table, 0.4 wt %of indium stearate is contained therein.

Evaluation on the moldability of the mixed powder was conducted withrespect to the test piece under the same conditions as Example 1, and,in addition, the compact molded into this test piece was sintered in abatch type atmospheric furnace at a sintering temperature of 1150° C.,sintering time of 60 min., and under a hydrogen gas atmosphere. Thedensity (SD) and the like of the sintered body are similarly shown inTable 5.

This sintered body was set inside a constant temperature and humiditychamber, and an atmospheric exposure test was conducted for 336 hours ata temperature of 40° C. and humidity of 95% in order to conduct amoisture and oxidation resistance experiment. The results of themoisture and oxidation resistance experiment are shown in Table 2. TABLE5 After Sintering at Pressure Before Sintering 1150° C., 1 hr, H2 SampleFill Pressure (Device side) φ t w GD Sintering φ t w SD No. No. Soap g t· cm−2 kgf · cm−2 mm mm g g/cc Batch mm mm g g/cc 231 (8) Co 1.5 6 4209.96 2.64 1.5 7.29 4-1 9.87 2.59 1.5 7.57 232 (8) Co 1.5 6 420 9.96 2.681.53 7.33 4-1 9.87 2.57 1.5 7.63 233 (8) Co 2.5 6 420 9.96 4.43 2.497.21 4-1 9.89 4.4 2.45 7.25 234 (8) Co 2.5 6 420 9.94 4.47 2.53 7.29 4-19.89 4.48 2.5 7.26 235 (8) Co 2.5 6 420 9.97 4.43 2.5 7.23 4-1 9.89 4.422.48 7.30 236 (8) Co 2.5 6 420 9.96 4.44 2.47 7.14 4-1 9.87 4.39 2.487.38 237 (8) Co 2.5 6 420 9.96 4.4 2.5 7.29 4-1 9.89 4.39 2.48 7.35 238(8) Co 2.5 6 420 9.94 4.39 2.47 7.25 4-1 9.9 4.32 2.45 7.37

Example 5

Synthesized copper stearate (Cu content of 12.0 wt %) was pulverized,and this was put through a sieve to obtain fine powder of 250 meshes orless.

0.4 wt % of this copper stearate (abbreviated as “Cu” in Table 6 below),0.4 wt % of the indium stearate obtained in Example 1 and 1.0 wt % ofgraphite powder were mixed with the iron powder (Hoganas-made: reducediron powder). This mixed powder (fill of 1.5 to 2.5 g) was molded into atest piece of approximately 10.05 mm 5×2.64 to 4.43 mmH under a moldingpressure of 6 t/cm².

In order to judge moldability, details of the relationship and the likeof the molding density (GD) and molding pressure of the respectivecompacts are shown in Table 6 (Sample No. 261 to 268). Further, althoughthe indium soap added together is not indicated in this Table, 0.4 wt %of indium stearate is contained therein.

Evaluation on the moldability of the mixed powder was conducted withrespect to the test piece under the same conditions as Example 1, and,in addition, the compact molded into this test piece was sintered in abatch type atmospheric furnace at a sintering temperature of 1150° C.,sintering time of 60 min., and under a hydrogen gas atmosphere. Thedensity (SD) and the like of the sintered body are similarly shown inTable 6.

This sintered body was set inside a constant temperature and humiditychamber, and an atmospheric exposure test was conducted for 336 hours ata temperature of 40° C. and humidity of 95% in order to conduct amoisture and oxidation resistance experiment. The results of themoisture and oxidation resistance experiment are shown in Table 2. TABLE6 After Sintering at Pressure Before Sintering 1150° C., 1 hr, H2 SampleFill Pressure (Device Side) φ t w GD Sintering φ t w SD No. No. Soap g t· cm−2 kgf · cm−2 mm mm g g/cc Batch mm mm g g/cc 261 (6) Cu 1.5 6 42010.05 2.69 1.47 6.89 4-2 10.04 2.62 1.45 6.99 262 (6) Cu 1.5 6 420 10.042.64 1.46 6.99 4-2 10.03 2.57 1.43 7.04 263 (6) Cu 2.5 6 420 10.04 4.422.44 6.97 4-2 10.04 4.39 2.4 6.91 264 (6) Cu 2.5 6 420 10.05 4.43 2.456.97 4-2 10.04 4.41 2.41 6.92 265 (6) Cu 2.5 6 420 10.04 4.41 2.45 7.024-2 10.04 4.4 2.4 7.03 266 (6) Cu 2.5 6 420 10.04 4.38 2.42 6.98 4-210.05 4.31 2.38 6.96 267 (6) Cu 2.5 6 420 10.06 4.34 2.4 6.96 4-2 10.034.29 2.36 6.96 268 (6) Cu 2.5 6 420 10.05 4.4 2.43 6.96 4-2 10.04 4.362.39 6.92

Example 6

Synthesized manganese stearate (Mn content of 12.0 wt %) was pulverized,and this was put through a sieve to obtain fine powder of 250 meshes orless.

0.4 wt % of this manganese stearate (abbreviated as “Mn” in Table 7below), 0.4 wt % of the indium stearate obtained in Example 1 and 1.0 wt% of graphite powder were mixed with the iron powder (Hoganas-made:reduced iron powder). This mixed powder (fill of 1.5 to 2.5 g) wasmolded into a test piece of approximately 10.05 mm φ×2.78 to 4.61 mmHunder a molding pressure of 6 t/cm².

In order to judge moldability, details of the relationship and the likeof the molding density (GD) and molding pressure of the respectivecompacts are shown in Table 7 (Sample No. 251 to 258). Further, althoughthe indium soap added together is not indicated in this Table, 0.4 wt %of indium stearate is contained therein.

Evaluation on the moldability of the mixed powder was conducted withrespect to the test piece under the same conditions as Example 1, and,in addition, the compact molded into this test piece was sintered in abatch type atmospheric furnace at a sintering temperature of 1150° C.,sintering time of 60 min., and under a hydrogen gas atmosphere. Thedensity (SD) and the like of the sintered body are similarly shown inTable 7.

This sintered body was set inside a constant temperature and humiditychamber, and an atmospheric exposure test was conducted for 336 hours ata temperature of 40° C. and humidity of 95% in order to conduct amoisture and oxidation resistance experiment. The results of themoisture and oxidation resistance experiment are shown in Table 2. TABLE7 After Sintering at Pressure Before Sintering 1150° C., 1 hr, H2 SampleFill Pressure (Device Side) φ t w GD Sintering φ t w SD No. No. Soap g t· cm−2 kgf · cm−2 mm mm g g/cc Batch mm mm g g/cc 251 (3) Mn 1.5 6 42010.07 2.78 1.54 6.96 4-2 10.05 2.77 1.51 6.87 252 (3) Mn 1.5 6 420 10.072.78 1.53 6.91 4-2 10.03 2.76 1.51 6.92 253 (3) Mn 2.5 6 420 10.05 4.612.54 6.95 4-2 10.07 4.56 2.49 6.86 254 (3) Mn 2.5 6 420 10.06 4.6 2.556.97 4-2 10.03 4.56 2.51 6.97 255 (3) Mn 2.5 6 420 10.04 4.59 2.53 6.964-2 10.04 4.56 2.48 6.82 256 (3) Mn 2.5 6 420 10.04 4.58 2.51 6.92 4-210.04 4.59 2.47 6.80 257 (3) Mn 2.5 6 420 10.05 4.57 2.51 6.92 4-2 10.034.52 2.47 6.92 258 (3) Mn 2.5 6 420 10.04 4.57 2.5 6.91 4-2 10.04 4.532.47 6.89

Comparative Example 1

Zinc stearate SZ-2000 (manufactured by Sakai Chemical Industry Co.,Ltd.) was used, and, as with Example 1, 0.8 wt % of this zinc stearate(abbreviated as “Zn” in Table 8 below) and 1.0 wt % of graphite powderwere mixed with the iron powder. This mixed powder (fill of 1.5 to 2.5g) was molded into a test piece of approximately 10.04 mm φ×2.73 to 4.58mmH under a molding pressure of 6 t/cm².

In order to judge moldability, moldability of the mixed powder wasevaluated under the same conditions as Example 1 with respect to thistest piece. Details of the relationship and the like of the moldingdensity (GD) and molding pressure of the respective compacts are shownin Table 8 (Sample No. 241 to 248).

Evaluation on the moldability of the mixed powder was conducted withrespect to the test piece under the same conditions as Example 1, and,in addition, the compact molded into this test piece was sintered in abatch type atmospheric furnace at a sintering temperature of 1150° C.,sintering time of 60 min., and under a hydrogen gas atmosphere. Thedensity (SD) and the like of the sintered body are similarly shown inTable 8.

This sintered body was set inside a constant temperature and humiditychamber, and an atmospheric exposure test was conducted for 336 hours ata temperature of 40° C. and humidity of 95% in order to conduct amoisture and oxidation resistance experiment. The results of themoisture and oxidation resistance experiment are shown in Table 2. TABLE8 After Sintering at Pressure Before Sintering 1150° C. 1 hr, H2 SampleFill Pressure (Device Side) φ t w GD Sintering φ t w SD No. No. Soap g t· cm−2 kgf · cm−2 mm mm g g/cc Batch mm mm g g/cc 241 (1) Zn 1.5 6 42010.05 2.78 1.51 6.85 4-2 10.03 2.73 1.49 6.91 242 (1) Zn 1.5 6 420 10.042.73 1.51 6.99 4-2 10.04 2.71 1.49 6.94 243 (1) Zn 2.5 6 420 10.03 4.512.5 7.02 4-2 10.04 4.47 2.46 6.95 244 (1) Zn 2.5 6 420 10.04 4.56 2.537.01 4-2 10.04 4.54 2.48 6.90 245 (1) Zn 2.5 6 420 10.04 4.5 2.5 7.024-2 10.03 4.47 2.45 6.94 246 (1) Zn 2.5 6 420 10.04 4.53 2.52 7.03 4-210.03 4.53 2.48 6.93 247 (1) Zn 2.5 6 420 10.05 4.58 2.53 6.96 4-2 10.034.54 2.49 6.94 248 (1) Zn 2.5 6 420 10.05 4.52 2.5 6.97 4-2 10.04 4.472.46 6.95

Comparative Example 2

Strontium stearate (Sr) was used, and, as with Example 1, 0.8 wt % ofthis strontium stearate (abbreviated as “Sr” in Table 9 below) and 1.0wt % of graphite powder were mixed with the iron powder. This mixedpowder (fill of 1.5 to 2.5 g) was molded into a test piece ofapproximately 10.35 mm φ×2.47 to 4.30 mmH under a molding pressure of 5t/cm², 6 t/cm², and 7 t/cm².

In order to judge moldability, moldability of the mixed powder wasevaluated under the same conditions as Example 1 with respect to thistest piece. Details of the relationship and the like of the moldingdensity (GD) and molding pressure of the respective compacts are shownin Table 9 (Sample No. 31 to 40).

Evaluation on the moldability of the mixed powder was conducted withrespect to the test piece under the same conditions as Example 1, and,in addition, the compact molded into this test piece was sintered in abatch type atmospheric furnace at a sintering temperature of 1150° C.,sintering time of 60 min., and under a hydrogen gas atmosphere. Thedensity (SD) and the like of the sintered body are similarly shown inTable 9.

As with Example 1, this sintered body was set inside a constanttemperature and humidity chamber, and an atmospheric exposure test wasconducted for 336 hours at a temperature of 40° C. and humidity of 95%in order to conduct a moisture and oxidation resistance experiment. Theresults of the moisture and oxidation resistance experiment are shown inTable 2. TABLE 9 Sample Fill Pressure φ t w GD φ t w SD No. No. Soap g t· cm−2 mm mm g g/cc mm mm g g/cc 31 (4) Sr 1.5 6 10.34 2.57 1.48 6.8610.34 2.57 1.47 6.81 32 (4) Sr 1.5 6 10.33 2.47 1.45 7.00 10.35 2.441.44 7.01 33 (4) Sr 2.5 6 10.36 4.29 2.49 6.89 10.37 4.24 2.46 6.87 34(4) Sr 2.5 6 10.36 4.25 2.45 6.84 10.35 4.22 2.42 6.82 35 (4) Sr 2.5 610.36 4.3 2.51 6.92 10.38 4.25 2.49 6.92 36 (4) Sr 2.5 6 10.35 4.1 2.416.99 10.34 4.06 2.39 7.01 37 (4) Sr 2.5 6 10.35 4.23 2.47 6.94 — — — —38 (4) Sr 2.5 6 10.35 4.22 2.46 6.93 — — — — 39 (4) Sr 2.5 5 10.34 4.262.43 6.79 10.35 4.19 2.4 6.81 40 (4) Sr 2.5 7 10.35 4.14 2.43 6.98 10.354.12 2.41 6.95

Comparative Example 3

Barium stearate (Ba) was used, and, as with Example 1, 0.8 wt % of thisbarium stearate (abbreviated as “Ba” in Table 10 below) and 1.0 wt % ofgraphite powder were mixed with the iron powder. This mixed powder (fillof 15 to 2.5 g) was molded into a test piece of approximately 10.35 mmφ××2.52 to 4.33 mmH under a molding pressure of 5 t/cm², 6 t/cm², and 7t/cm². In order to judge moldability, moldability of the mixed powderwas evaluated under the same conditions as Example with respect to thistest piece. Details of the relationship and the like of the moldingdensity (GD) and molding pressure of the respective compacts are shownin Table 10 (Sample No. 41 to 50).

Evaluation on the moldability of the mixed powder was conducted withrespect to the test piece under the same conditions as Example 1, and,in addition, the compact molded into this test piece was sintered in abatch type atmospheric furnace at a sintering temperature of 1150° C.,sintering time of 60 min., and under a hydrogen gas atmosphere. Thedensity (SD) and the like of the sintered body are similarly shown inTable 10.

As with Example 1, this sintered body was set inside a constanttemperature and humidity chamber, and an atmospheric exposure test wasconducted for 336 hours at a temperature of 40° C. and humidity of 95%in order to conduct a moisture and oxidation resistance experiment. Theresults of the moisture and oxidation resistance experiment are shown inTable 2. TABLE 10 Sample Fill Pressure φ t w GD φ t w SD No. No. Soap gt · cm−2 mm mm g g/cc mm mm g g/cc 41 (5) Ba 1.5 6 10.35 2.52 1.48 6.9810.34 2.5 1.47 7.00 42 (5) Ba 1.5 6 10.34 2.52 1.46 6.90 10.35 2.48 1.456.95 43 (5) Ba 2.5 6 10.35 4.28 2.5 6.94 10.38 4.22 2.47 6.92 44 (5) Ba2.5 6 10.35 4.33 2.54 6.97 10.35 4.33 2.51 6.89 45 (5) Ba 2.5 6 10.354.29 2.48 6.87 10.34 4.24 2.46 6.91 46 (5) Ba 2.5 6 10.35 4.31 2.51 6.9210.35 4.29 2.48 6.87 47 (5) Ba 2.5 6 10.35 4.25 2.49 6.96 — — — — 48 (5)Ba 2.5 6 10.35 4.22 2.47 6.96 — — — — 49 (5) Ba 2.5 5 10.35 4.32 2.496.85 10.35 4.25 2.47 6.91 50 (5) Ba 2.5 7 10.35 4.26 2.53 7.06 10.354.25 2.5 6.99

Comparative Example 4

Stearic acid (Ce, La, Nd, Pr) (rare earth) was used, and, as withExample 1, 0.8 wt % of this stearic acid (Ce, La, Nd, Pr) (abbreviatedas “RE” in Table 11 below) and 1.0 wt % of graphite powder were mixedwith the iron powder (Ce 6.2 wt %, La 3.4 wt %, Nd 1.8 wt %, Pr 0.6 wt%). This mixed powder (fill of 1.5 to 2.5 g) was molded into a testpiece of approximately 10.35 mm φ×2.55 to 4.29 mmH under a moldingpressure of 5 t/cm², 6 t/cm², and 7 t/cm². In order to judgemoldability, details of the relationship and the like of the moldingdensity (GD) and molding pressure of the respective compacts are shownin Table 11 (Sample No. 51 to 60).

Evaluation on the moldability of the mixed powder was conducted withrespect to the test piece under the same conditions as Example 1, and,in addition, the compact molded into this test piece was sintered in abatch type atmospheric furnace at a sintering temperature of 1150° C.,sintering time of 60 min., and under a hydrogen gas atmosphere. Thedensity (SD) and the like of the sintered body are similarly shown inTable 11.

As with Example 1, this sintered body was set inside a constanttemperature and humidity chamber, and an atmospheric exposure test wasconducted for 336 hours at a temperature of 40° C. and humidity of 95%in order to conduct a moisture and oxidation resistance experiment. Theresults of the moisture and oxidation resistance experiment are shown inTable 2. TABLE 11 Sample Fill Pressure φ t w GD φ t w SD No. No. Soap gt · cm−2 mm mm g g/cc mm mm g g/cc 51 (6) RE 1.5 6 10.36 2.6 1.5 6.8410.35 2.56 1.48 6.87 52 (6) RE 1.5 6 10.35 2.55 1.48 6.90 10.36 2.531.47 6.89 53 (6) RE 2.5 6 10.36 4.2 2.46 6.95 10.36 4.17 2.45 6.97 54(6) RE 2.5 6 10.35 4.31 2.48 6.84 10.35 4.25 2.5 6.99 55 (6) RE 2.5 610.36 4.2 2.47 6.98 10.34 4.16 2.45 7.01 56 (6) RE 2.5 6 10.36 4.23 2.486.96 10.35 4.2 2.47 6.99 57 (6) RE 2.5 6 10.36 4.16 2.45 6.99 — — — — 58(6) RE 2.5 6 10.35 4.25 2.51 7.02 — — — — 59 (6) RE 2.5 5 10.35 4.292.47 6.84 10.34 4.25 2.46 6.89 60 (6) RE 2.5 7 10.35 4.1 2.44 7.07 10.344.06 2.41 7.07

Comparative Example 5

Furthermore, additive-free iron powder (Hoganas-made: reduced ironpowder (fill of 1.5 to 2.5 g)) was molded into a test piece ofapproximately 9.96 mm φ×2.61 to 4.46 mmH under a molding pressure of 5t/cm², 6 t/cm², and 7 t/cm². In order to judge moldability, details ofthe relationship and the like of the molding density (GD) and moldingpressure of the respective compacts are shown in Table 12 (Sample No.301 to 308).

Evaluation on the moldabilty of the mixed powder was conducted withrespect to the test piece under the same conditions as Example 1, and,in addition, the compact molded into this test piece was sintered in abatch type atmospheric furnace at a sintering temperature of 1150° C.,sintering time of 60 min., and under a hydrogen gas atmosphere. Thedensity (SD) and the like of the sintered body are similarly shown inTable 12.

As with Example 1, this sintered body was set inside a constanttemperature and humidity chamber, and an atmospheric exposure test wasconducted for 336 hours at a temperature of 40° C. and humidity of 95%in order to conduct a moisture and oxidation resistance experiment. Theresults of the moisture and oxidation resistance experiment are shown inTable 2. TABLE 12 After Sintering at Pressure Before Sintering 1150° C.,1 hr, H2 Sample Fill Pressure (Device Side) φ t w GD Sintering φ t w SDNo. No. Soap g t · cm−2 kgf · cm−2 mm mm g g/cc Batch mm mm g g/cc 301(2) None 1.5 6 420 10.07 2.72 1.47 6.79 4-3 10.06 2.7 1.5 6.99 302 (2)None 1.5 6 420 10.07 2.66 1.44 6.80 4-3 10.06 2.64 1.48 7.05 303 (2)None 2.5 6 420 10.08 4.38 2.44 6.98 4-3 10.05 4.37 2.46 7.10 304 (2)None 2.5 6 420 10.05 4.48 2.49 7.01 4-3 10.05 4.45 2.52 7.14 305 (2)None 2.5 6 420 10.06 4.47 2.48 6.98 4-3 10.05 4.45 2.5 7.15 306 (2) None2.5 6 420 10.05 4.42 2.44 6.96 4-3 10.05 4.41 2.46 7.03 307 (2) None 2.56 420 10.06 4.44 2.45 6.95 4-3 10.04 4.43 2.46 7.01 308 (2) None 2.5 6420 10.05 4.44 2.45 6.96 4-3 10.04 4.42 2.48 7.09

As evident from Tables 1 to 12, from the evaluation results ofcompressibility, an approximately even powder density was obtained.Further, the extraction pressure (kg) after molding is shown in Table13, and the compact of the present invention to which metallic soap hasbeen added has lower extraction pressure in comparison to anadditive-free compact, and extraction pressure roughly equivalent tozinc stearate can be obtained.

As described above, Examples 1 to 6 of the present invention to whichmetallic soap has been added have roughly the same lubricity andmoldability as Comparative Example 1 to which a zinc stearate lubricanthas been added thereto. TABLE 13 Extraction Pressure (kg) MoldingMolding Molding Rustproof Pressure 5 Pressure 6 Pressure 7 Lubricant(t/cm²) (t/cm²) (t/cm²) Material 5 6 7 (1) Zn Stearate 301 384 431 (2)Mn Stearate 352 359 363 (3) Bi Stearate 316 350 383 (4) Ni Stearate 318377 402 (5) Cu Stearate 371 370 364 (6) Al Stearate 343 361 372 (7) CoStearate 322 382 429 (8) In Stearate 345 340 396 (9) None 639 812 914

Next, as evident from Table 2 regarding Comparative Example 5 in which alubricant was not added to the iron powder, in the moisture resistanceand oxidation resistance experiment after sintering, change in color(corrosion) occurred after 96 hours (4 days), and, together with thelapse in time, the degree of change in color increased gradually. Thechange in color was severe after 336 hours.

Meanwhile, with the strontium stearate of Comparative Example 2, thecolor changed even more in comparison to the foregoing additive-freeComparative Example 5, and the color changed severely with the lapse intime. Further, with the stearic acid (Ce, La, Nd, Pr) (rare earth) ofComparative Example 4, the color changed severely after 96 hours (4days). Accordingly, the strontium stearate of Comparative Example 2 andthe stearic acid (Ce, La, Nd, Pr) (rare earth) of Comparative Example 4are not as effective in rust prevention in comparison to the case whenno additive is added.

Contrarily, the zinc stearate of Comparative Example 1 and the bariumstearate of Comparative Example 3 were approximately equivalent to theadditive-free Comparative Example 5 even after the lapse of 336 hours,and it is evident that the addition of zinc stearate and barium stearatehas not effect with respect to moisture resistance and oxidationresistance.

Meanwhile, it is clear that each of the Examples 1 to 6 to which themetallic soap has been added thereto according to the present inventiononly has a slight change in color from the foregoing moisture resistanceand oxidation resistance experiment after the lapse of 336 hours, andeach of such Examples has moisture resistance and oxidation resistanceproperties.

Although there is no special description regarding examples of addingaluminum soap, or adding a compound of bismuth soap, nickel soap, cobaltsoap, copper soap, manganese soap and aluminum soap to the indium soap,the same results were obtained as with Examples 1 to 6 for each of theforegoing examples.

Accordingly, the mixed powder for powder metallurgy obtained by addingthe metallic soap of the present invention to metallic powder for powdermetallurgy having iron as its principal component has favorablemoldability, and it has been further confirmed that it possessesfavorable moisture resistance and oxidation resistance properties.

Further, the electrode potential in a case of employing the indium soap,bismuth soap, manganese soap and zinc soap of the present invention wasmeasured. As the measurement conditions, solution:0.03MFeSO₄+0.47MK₂SO₄; pH: 4.56; liquid temperature: 23.1; and referenceelectrode: SSE (Ag/AgCl) were used.

The result was bismuth addition: −604.73 mV; indium addition: −614.33mV; manganese addition: −628.93 mV; and zinc addition: −631.87 mV, andthe obtained tendency was that higher the potential, the less generationof rust in the environment experiment. This roughly coincides with thetrend of the moisture resistance and oxidation resistance aftersintering shown in Table 2.

Effect of the Invention

As described above, by employing mixed powder for powder metallurgyobtained by adding the metallic soap of the present invention tometallic powder for powder metallurgy having iron as its principalcomponent, the rustproof effect of sintered bodies such as sinteredmechanical components, sintered oil retaining bearings, metal graphitebrushes and so can thereby be improved remarkably.

1. Metallic powder for powder metallurgy, comprising a metal powderhaving iron as its principal component, and containing indium soap. 2.Metallic powder for powder metallurgy according to claim 1, wherein saidmetal powder contains at least one additional type of soap selected fromthe group consisting of bismuth soap, nickel soap, cobalt soap, coppersoap, manganese soap and aluminum soap.
 3. A rustproof iron-basedsintered body prepared by a process comprising the steps of: addingindium soap to a metallic powder for powder metallurgy to form amixture, said metallic powder having iron as its principal component,and after said adding step, sintering said mixture.
 4. A rustproofiron-based sintered body according to claim 3, wherein, before saidsintering step, at least one additional type of soap selected from thegroup consisting of bismuth soap, nickel soap, cobalt soap, copper soap,manganese soap and aluminum soap is added to said metallic powder.